Tissue-type plasminogen activator is a target of the tumor suppressor gene maspin

Maspin Expression Is Transactivated by p63 and Is Critical for the Modulation of Lung Cancer Progression

Maspin inhibits metastasis of some cancer cells, and clinical studies have identified correlations between maspin loss and poor prognosis in several cancer types. Maspin was found to be significantly overexpressed in lung cancer samples as compared with matched normal lung tissues. However, the regulatory mechanism of maspin expression remains unclear. We show here that differential expression of maspin in carcinoma-derived lung cancer cells is regulated at the transcriptional level. We found that p63 is a critical factor for the transcription of maspin, which is lost in highly invasive cancer cells such as NCI-H157, NCI-322, and NCI-358. No correlation was found between maspin expression and the previously associated transcription factors, p53, Ets1, and Pdef. Instead, maspin expression was strictly dependent on the presence of p63 in lung cancer tissues (P < 0.001) and in the tested cell lines. Transient expression of p63 transactivated the maspin promoter with remarkable fold changes in cells expressing the TAp63, suggesting that TAp63 might be a novel stimulator of the maspin promoter in lung cancer. We have also demonstrated the binding of p63 protein to a previously identified p53-binding site on the maspin promoter by gel shift and chromatin immunoprecipitation assays. In tumor tissues, maspin expression was associated with lymph node involvement (P = 0.035) and tumor stage (P = 0.063) in all tested cases, except squamous carcinoma. In terms of function, ectopic expression of maspin inhibited cell invasion in squamous carcinoma as well as adenocarcinoma. Taken together, these results define maspin as a new molecular target of p63 that eventually inhibits the invasion of lung cancer.

Discrepancy between mRNA and protein expression of tumour suppressor maspin in synovial tissue may contribute to synovial hyperplasia in rheumatoid arthritis

OBJECTIVE

To investigate the expression of maspin in RA synovial tissue and compare it with the expression in osteoarthritis (OA) and normal synovial tissue (NS).

METHODS

Using specific primers for maspin, a 237 bp fragment was amplified from cDNA obtained from cultured RA, OA, and normal synovial fibroblasts (SF) by RT-PCR. Additionally, mRNA expression levels were determined quantitatively by real time PCR. mRNA expression of maspin was investigated on snap frozen and paraffin embedded synovial tissue sections by in situ hybridisation. Immunohistochemistry was used to identify the cell type expressing maspin. SDS-PAGE and western blotting were performed to evaluate the protein expression in cultured SF. To confirm protein synthesis in situ, immunohistochemistry with specific anti-maspin antibodies was performed in synovial tissue sections of patients with RA.

RESULTS

RT-PCR showed expression of maspin in all cDNA samples from cultured SF. Maspin mRNA was found to be decreased in RA SF twofold and 70-fold compared with OA SF and NS SF, respectively. Maspin mRNA was expressed in RA, OA, and normal synovial tissue. Importantly, maspin transcripts were also found at sites of invasion into cartilage and bone. At the protein level, maspin could be detected in RA and, less prominently, OA SF. In RA synovial tissue, maspin protein was detected in only a few synovial lining cells.

CONCLUSION

Maspin is expressed intensively in RA SF at the mRNA level, but only slightly at the protein level, possibly owing to down regulation of maspin; this may contribute to the hyperplasia of synovial tissue in RA.

Expression of Maspin in non-muscle invasive bladder carcinoma: correlation with tumor angiogenesis and prognosis

OBJECTIVES

Maspin is a member of the serpin (serine protease inhibitor) family and has been shown to be a suppressor of tumor growth and an inhibitor of angiogenesis as well as metastasis in several types of tumors. We studied expression patterns of Maspin in pTa/pT1 urothelial carcinoma of the bladder and compared them with microvessel density (MVD) for two vascular markers (CD34 and CD105) and correlated the findings with clinical outcome.

MATERIAL AND METHODS

We investigated tumor samples of 110 patients undergoing transurethral resection for pTa/pT1 bladder carcinoma (pTa, n=84; pT1, n=26; grade 1, n= 22; grade 2, n= 81; grade 3, n=7). Immunohistochemical studies were performed using the monoclonal antibodies, anti-human Maspin (NCL Maspin), anti-CD34 Class II and anti-CD105. Maspin expression level was classified according to the staining intensity (- to +++). The blood vessels (CD34) and specifically proliferating blood vessels (CD105) were counted as vessels per field (microvessel density, MVD).

RESULTS

Of the 110 tumors, 27 showed a negative immunostaining for Maspin, 46 tumors stained +, 29 stained ++, and 8 stained +++. Maspin expression correlated inversely with CD34 reactivity. In tumors with loss of or only weak Maspin expression, the MVD for CD34 was 21.7 vessels per field, and 4.2 vessels per field for proliferating vessels (CD105), whereas Maspin-positive tumors had an MVD of 17.7 vessels per field (CD34), and of 6.0 vessels per field (CD105). Complete follow-up data are available in 92 patients. After a median follow-up of 25 months, 18 of the 92 patients (19.6%) had tumor recurrences. Tumors with decreased Maspin expression (-/+) had a shorter disease-free interval (23 months) than patients with stronger Maspin (++/+++) expression (29 months), whereas a Kaplan-Meier analysis and the log-rank test showed no significant difference in disease-free survival between the patients.

CONCLUSION

The clinical importance of Maspin has been mainly investigated regarding tumor progression or metastasis. We found a decreased Maspin expression in a large portion of pTa/pT1 bladder tumors. Even if patients with decreased Maspin expression have a slightly shorter disease-free survival Maspin does not appear to be a promising prognostic marker.

Pathobiological significance of vascular endothelial growth factor and Maspin expressions in human gastric carcinoma

AIM: To investigate the correlation between expression of vascular endothelial growth factor (VEGF) and cell differentiation, invasion, metastasis and Maspin expression in gastric carcinoma.

METHODS: Formalin-fixed paraffin-embedded tissue specimens from 73 cases of gastric carcinoma were studied with SP immunohistochemistry, using anti-VEGF monoclonal antibody, and thirty-nine of them were studied using anti-Maspin monoclonal antibody. VEGF expression was compared with the clinical stage, lymph node metastasis, and Borrmann's and WHO's classification of gastric carcinoma.

RESULTS: The positive rate of VEGF expression was significantly higher in adjacent non-carcinoma epithelia (ANCE) than in non-metaplastic, non-carcinoma gastric epithelia (NMNCE), which were at least 4 cm distant from the primary tumor (P = 0.000, χ² = 73.03). The positive rate of VEGF expression was significantly higher in advanced gastric carcinoma (AGC) than in early gastric carcinoma (EGC) (P = 0.032, χ² = 4.62). The positive rate of VEGF expression in gastric carcinomas with lymph node metastases was significantly higher than that in those without metastasis (P = 0.006, χ² = 7.47). Maspin was weakly expressed in 16 out of 39 cases of NMNCE, and the positive immunoreaction was limited to gland cells of the stomach body. There was no significant correlation between the expression of VEGF and histological or gross classifications, and correlation between the expressions of VEGF and Maspin in gastric carcinoma (P = 0.648, χ² = 0.21).

CONCLUSION: Expression of VEGF is significantly correlated to the malignant biological behaviors of gastric carcinoma, but there is no significant correlation between the expression of VEGF and Maspin.

Do antiangiogenic protein fragments have amyloid properties?

Tumor growth requires proteolytic activity. As a consequence, protein breakdown products are present in the circulation of patients with cancer. Within the past decade a large number of proteolytic fragments have been identified that inhibit angiogenesis and tumor growth. The mechanism of action of these inhibitors is still poorly understood. We recently found that the effects of the angiogenesis inhibitor endostatin on endothelial cells is critically dependent on the presence of cross-beta structure, a structure also present in amyloidogenic polypeptides in plaques of patients with amyloidosis, such as Alzheimer disease. We also showed that cross-beta structure containing endostatin is a ligand for tissue-type plasminogen activator (tPA). We noted that many angiogenesis inhibitors stimulate tPA-mediated plasminogen activation. Because the presence of cross-beta structure is the common denominator in tPA-binding ligands, we hypothesize that these endogenous antiangiogenic proteolytic fragments share features with amyloidogenic polypeptides. We postulate that the cross-beta structural fold is present in these antiangiogenic polypeptide fragments and that this structure mediates the inhibitory effects. The hypothesis provides new insights in the potential mechanisms of these angiogenesis inhibitors and offers opportunities to improve their use.

Aberrant Expression of the Maspin Gene Associated with Epigenetic Modification in Melanoma Cells

Maspin, a mammary serine protease inhibitor, was originally reported to be a tumor suppressor gene in breast and prostate cancers. The expression pattern of the maspin gene differs among cancer types and normal tissue however, and its significance as a tumor suppressor has been questioned. In this study, maspin expression and/or allele-specific methylation status were investigated in five melanoma cell lines and a normal human epidermal melanocyte (NHEM) cell line, and 80 surgically resected tumors (40 melanomas and 40 melanocytic nevi). One (HMV-I) of five melanoma cell lines overexpressed maspin protein whereas the remaining four melanoma cell lines and NHEM did not. The 19 CpG sites of the maspin promoter region were extensively hypomethylated in HMV-I, a maspin-positive cell line, and those of the remaining four melanoma and NHEM cell lines were hypermethylated. Furthermore, maspin-negative cell lines exhibited activation after treatment with 5-aza-2'-deoxycytidine, a DNA demethylating agent. Immunoreactivity for maspin was negative in normal skin melanocytes and 40 melanocytic nevi, but five (12.5%) of 40 melanomas were positive. The methylation status judged by the methylation-specific PCR method was inversely correlated with maspin protein expression in vitro and in vivo. These results suggest that maspin expression in normal skin melanocytes and melanocytic nevi may be repressed in a cell-type-specific manner, whereas maspin is expressed aberrantly in a subset of melanoma cells by epigenetic modification. Further investigations are required to determine the significance of aberrant maspin expression.

Cell-type-specific repression of the maspin gene is disrupted frequently by demethylation at the promoter region in gastric intestinal metaplasia and cancer cells

Maspin, a serine protease inhibitor, was originally reported as a tumor suppressor gene in breast and prostatic cancers. We examined maspin expression and/or the allele-specific methylation status in four gastric cancer cell lines, as well as normal, metaplastic, and cancerous epithelia obtained from 50 gastric cancer patients. Three gastric cancer cell lines exhibiting maspin overexpression showed hypomethylation at either both alleles or a haploid allele. Only one cell line (GCIY) was maspin-negative but maspin expression was reactivated after treatment with a demethylating agent, 5-aza-2'-deoxycytidine. Dense and diffuse immunoreactivity for maspin was observed in 40 (80%) of 50 gastric cancers and all gastric normal epithelia (GNE) with intestinal metaplasia (IM), but not in GNE without IM. We further analyzed the allele-specific methylation status in 10 of 50 cases subjected to immunohistochemistry by the crypt isolation technique followed by a bisulfite genome sequencing method. The maspin gene promoter region of all GNE without IM was hypermethylated on both alleles whereas those with IM frequently represented the haploid type of hypomethylation status. In six of seven gastric cancers in which crypt isolation was possible, demethylation frequently occurred and extended to both alleles. Maspin mRNA was amplified from GNE with IM and cancerous crypts but not from GNE without IM. These results suggest that demethylation at the maspin gene promoter disrupts the cell-type-specific gene repression in both GNE and gastric cancer.

Clinicopathological significance and molecular regulation of maspin expression in ductal adenocarcinoma of the pancreas

We evaluated the biological relevance of maspin expression in pancreatic ductal adenocarcinoma and studied regulatory mechanisms of maspin gene activation in pancreatic carcinoma cell lines. Maspin expression was immunohistochemically detected in a series of 57 pancreatic ductal adenocarcinomas, 51 (90%) of which were classified as high-expressers. In lymph node metastases, maspin expression was somewhat decreasingly found in 39/49 (80%). Maspin high-expressers showed predominantly a low histological grade (p=0.013). Moreover, maspin expression was found in two mixed ductal-endocrine carcinomas, but not in 10 endocrine tumors and the surrounding normal pancreatic tissues. Using a luciferase reporter system, maspin promoter activity was induced in the maspin-positive pancreatic cancer cell lines as well as maspin-negative PANC-1 cells. Additionally, treatment with the DNA methyltransferase inhibitor, 5-aza-2' deoxycytidine, and histone deacetylase inhibitor, trichostatin A, led to re-expression of maspin mRNA in PANC-1 cells. Our results indicate that maspin expression is up-regulated in most if not all pancreatic ductal adenocarcinomas and may be related to the development and differentiation, and that DNA methylation and histone deacetylation may suppress maspin gene activation in pancreatic cancer cells.

Expression of maspin is up-regulated during the progression of mammary ductal carcinoma

AIMS

The tumour suppressor gene maspin is reported to inhibit the motility, invasiveness and metastasis of breast cancer cells. Maspin is expressed in normal mammary myoepithelial cells but is down-regulated during the progression of ductal carcinoma. However, we recently reported that maspin expression was frequently observed in invasive ductal carcinoma (IDC) with an aggressive phenotype, and it was a strong indicator of a poor prognosis. To our knowledge, to date, there has been no report investigating maspin expression in a large series of ductal carcinoma in situ (DCIS).

METHODS AND RESULTS

To clarify whether there is down-regulation during the progression of ductal carcinoma, we immunohistochemically investigated the expression of maspin in 145 DCIS, 92 invasive ductal carcinomas with a predominant intraductal component as well as 94 usual ductal hyperplasias and 27 atypical ductal hyperplasias. The expression of maspin in carcinoma cells was observed in 9.6% (14 of 145) of DCIS and 18.5% (17 of 92) of IDC with a predominant intraductal components. It significantly correlated with larger tumour size (P = 0.013; P = 0.042), higher histological grade (P = 0.015; P = 0.0003) and the presence of comedo-necrosis (P = 0.000005; P = 0.0074) in DCIS and IDC with a predominant intraductal components, respectively. In epithelial cells, the expression of maspin was observed in only one case of usual ductal hyperplasia, and all cases of atypical ductal hyperplasia were negative.

CONCLUSIONS

These results and our previous investigation in which 27.4% of IDC were positive for maspin suggest that the expression of maspin in epithelial cells could be up-regulated during the progression of ductal carcinoma, and that it could be correlated with the acquisition of an aggressive phenotype.

Prognostic value of maspin mRNA expression in ER alpha-positive postmenopausal breast carcinomas

Maspin, a member of the serpin family, has a role in cell migration, angiogenesis and apoptosis. Little is known of the clinical significance of maspin gene expression in human cancers. We developed a real-time quantitative RT-PCR assay to quantify the full range of maspin mRNA copy numbers in a series of 10 ER alpha-positive and 10 ER alpha-negative breast tumours. We observed a statistical link between low maspin mRNA levels and positive oestrogen status (P=0.0012). In consequence, to better assess the prognostic value of maspin gene expression in breast cancer, we then quantified maspin mRNA content in an additional independent well-defined cohort of 105 ER alpha-positive postmenopausal breast cancer patients treated with primary surgery followed by adjuvant tamoxifen alone. Maspin expression varied widely in tumour tissues (by nearly four orders of magnitude), being underexpressed in 33 out of 105 tumours (31.4%) and overexpressed in 24 out of 105 tumours (22.9%) relative to normal breast tissues. Immunohistochemical studies demonstrated that maspin protein was strictly expressed in myoepithelial cells of normal breast tissue and in tumour epithelial cells, exclusively in maspin-overexpressing tumours. Patients with tumours overexpressing the maspin gene had significantly shorter relapse-free survival after surgery than patients whose tumours normally expressed or underexpressed maspin (P=0.0011). The prognostic significance of maspin overexpression persisted in Cox multivariate regression analysis (P=0.0024). These findings show that the maspin mRNA level can have important prognostic significance in human breast cancer, and point to the maspin gene as a putative molecular predictor of hormone responsiveness in breast cancer.

Maspin functions as tumor suppressor by increasing cell adhesion to extracellular matrix in prostate tumor cells

PURPOSE

Maspin, a unique member of the serine protease inhibitor family, shows tumor suppressing activity for breast cancer progression and metastasis. Few studies have directly linked maspin function to prostate cancer. We used prostate tumor cells derived from the TRAMP (transgenic adenocarcinoma of mouse prostate) prostate tumor model to study the tumor suppressive function of maspin in prostate cancer.

MATERIALS AND METHODS

Maspin cDNA was introduced via a retroviral plasmid into TRAMP C2N prostate tumor cells, which are aggressive and invasive in nature. We investigated the tumorigenesis of these stable cell lines in vitro by assessing the growth rate, anchorage independence and adhesion to extracellular matrix proteins such as fibronectin and laminin.

RESULTS

Stable cell lines expressing maspin had decreased tumorigenic potential, as assessed by anchorage independent growth in soft agar assay compared with controls. Maspin stable transfectants showed decreased metastatic potential, as evaluated by modified Boyden chamber assay and increased adhesion to fibronectin and laminin.

CONCLUSIONS

Our study confirms that maspin has a tumor suppressive role not only in breast cancer, but also in prostate cancer. The data in this study suggest that maspin can decrease the tumorigenic and metastatic potential of prostate tumors, most probably by remodeling cell-extracellular matrix interactions or triggering extracellular matrix mediated signaling pathways that negatively regulate tumor migration and invasion.

Inhibition of the cysteine proteinases cathepsins K and L by the serpin headpin (SERPINB13): a kinetic analysis

Headpin (SERPINB13) is a novel member of the serine proteinase inhibitor (Serpin) gene family that was originally cloned from a keratinocyte cDNA library. Western blot analysis using a headpin-specific antiserum recognized a protein with the predicted M(r) of 44kDa in lysates derived from a transformed keratinocyte cell line known to express headpin mRNA. Similarity of the reactive-site loop (RSL) domain of headpin, notably at the P1-P1(') residues, with other serpins that inhibit cysteine and serine proteinases suggests that headpin may inhibit similar proteinases. This study demonstrates that recombinant headpin indeed inhibits cathepsins K and L, but not chymotrypsin, elastase, trypsin, subtilisin A, urokinase-type plasminogen activator, plasmin, or thrombin. The second-order rate constants (k(a)) for the inhibitory reactions of rHeadpin with cathepsins K and L were 5.1+/-0.6x10(4) and 4.1+/-0.8x10(4)M(-1)s(-1), respectively. Headpin formed SDS-stable complexes with cathepsins K and L, a characteristic property of inhibitory serpins. Interactions of the RSL domain of headpin with cathepsins K and L were indicated by cleavage of headpin near the predicted P1-P1(') residues by these proteinases. These results demonstrate that the serpin headpin possesses specificity for inhibiting lysosomal cysteine proteinases.

Maspin inhibits cell migration in the absence of protease inhibitory activity

Maspin is a member of the serpin family of protease inhibitors and is a tumor suppressor gene acting at the level of tumor invasion and metastasis. This in vivo activity correlates with the ability of maspin to inhibit cell migration in vitro. This behavior suggests that maspin inhibits matrix-degrading proteases, such as those of the plasminogen activation system, in a similar manner to the serpin PAI-1. However, there is controversy concerning the protease inhibitory activity of maspin. It is devoid of activity against a wide range of proteases, in common with other non-inhibitory serpins, but has recently been reported to inhibit plasminogen activators associated with cells and other biological surfaces (Sheng, S. J., Truong, B., Fredrickson, D., Wu, R. L., Pardee, A. B., and Sager, R. (1998) Proc. Natl. Acad. Sci. U. S. A. 95, 499-504; McGowen, R., Biliran, H., Jr., Sager, R., and Sheng, S. (2000) Cancer Res. 60, 4771-4778). We have compared the effects of maspin with those of PAI-1 in a range of situations in which plasminogen activation is potentiated, reflecting the biological context of this proteolytic system: urokinase-type plasminogen activator bound to its receptor on the surface of tumor cells, tissue-type plasminogen activator specifically bound to vascular smooth muscle cells, fibrin, and the prion protein. Maspin was found to have no inhibitory effect in any of these situations, in contrast to the efficient inhibition observed with PAI-1, but nevertheless maspin inhibited the migration of both tumor and vascular smooth muscle cells. We conclude that maspin is a non-inhibitory serpin and that protease inhibition does not account for its activity as a tumor suppressor.

Expression and regulation of tumor suppressor gene maspin in breast cancer

Maspin (mammary serpin) is an inhibitor of serine proteases with tumor suppressor activity in breast cancer. Maspin was originally identified by subtractive hybridization in normal breast epithelial cells, but its expression decreased during tumor progression. The loss of maspin gene expression with increasing malignancy is by transcriptional regulation. Maspin is known to be involved in invasion and metastasis, interact with the p53 tumor suppressor pathway, and act as an inhibitor of angiogenesis. The immunohistochemical analysis and reverse-transcription polymerase chain reaction of maspin in normal human breast tissue and breast carcinoma indicated a stepwise reduction of maspin expression during the progression from ductal carcinoma in situ to invasive carcinoma to lymph node metastasis. The lack of maspin expression in breast cancer seems to be associated with a short disease-free survival and supports maspin's function as an indicator for tumor aggressiveness and metastatic potential. New studies on the gene regulation of maspin provide evidence for promising potential of possible re-expression of maspin in tumor cells. The function of maspin as a tumor suppressor gene involved in tumor invasion, metastasis, and angiogenesis may not be limited to breast cancer.

Expression of maspin predicts poor prognosis in breast-cancer patients

The tumor suppressor gene maspin has been reported to inhibit the invasiveness and motility of breast cancer cells. It has been reported that maspin is expressed in normal human mammary epithelial cells but is downregulated during cancer progression, and that p53 could induce maspin expression by transcriptional activation. However, to date, the clinical significance of maspin expression and its correlation with p53 protein expression in human breast cancer patients have not been elucidated. One hundred and sixty-eight female patients diagnosed with invasive ductal carcinoma, who had undergone a mastectomy (154 patients) or breast-conserving surgery (14 patients), were followed up for 15-119 months (median: 87 months) postoperatively. Immunoreactivity for maspin and p53 antibodies with paraffin-embedded carcinoma tissue was investigated using labeled streptavidin-biotin methods. Tumors with more than 20% of positive cells were considered positive for the expression of maspin. The expression of maspin in carcinoma cells was found in 27.4% (46 of 168) and significantly correlated with larger tumor size (p = 0.008), higher histologic grade (p = 0.0001) and positive p53 status (p = 0.003). A significant inverse relationship was observed between the expression of maspin and estrogen receptor (p = 0.0004) or progesterone receptor status (p = 0.02). Univariate analysis by log-rank test revealed a significant association between the expression of maspin and shorter relapse-free survival (p < 0.0001) and overall survival (p < 0.0001). According to Cox's multivariate analysis, the expression of maspin had the most significant effect in relapse-free survival (p < 0.0001) and overall survival (p < 0.0001) followed by lymph node status. In turn, the expression of maspin in 58 cases of ductal carcinoma in situ were also investigated to explore whether the downregulation of maspin through cancer progression are true or not. However, there were no positive cases in our series. These results seem to be contrary to previous reports defining maspin as a tumor suppressor gene. Although more precise characterization of the maspin expression, especially gene analysis is essential, the present investigation suggests that the expression of maspin is not downregulated through malignant progression and that the immunohistochemic detection of maspin in carcinoma cells may be helpful for selecting the group of breast cancer patients with an aggressive phenotype.

Maspin sensitizes breast carcinoma cells to induced apoptosis

Maspin, a novel serine protease inhibitor (serpin), suppresses the growth and metastasis of breast tumor in vivo. However, the underlying molecular mechanism is unclear. In the current study, we report the first evidence that endogenous maspin expression in mammary carcinoma cells MDA-MB-435 enhanced staurosporine (STS)-induced apoptosis as judged by the increased fragmentation of DNA, increased proteolytic inactivation of poly-[ADP-ribose]-polymerase (PARP), as well as the increased activation of caspase-8 and caspase-3. In parallel, recombinant maspin did not directly regulate the proteolytic activities of either caspase-3 or caspase-8 in vitro. Consistent with this result, maspin expressing normal mammary epithelial cells underwent more rapid STS-induced apoptosis as compared to breast carcinoma cells. Interestingly, maspin transfectant cells did not undergo spontaneous apoptosis in the absence of STS. Moreover, neither purified maspin protein added from outside nor endogenous maspin secreted to the cell culture media sensitized cells to STS-induced apoptosis. To investigate the structural determinants of maspin in its apoptosis-sensitizing effect, MDA-MB-435 cells were also transfected with maspin/PAI-1 and PAI-1/maspin chimeric constructs resulting from swapping the N-terminal and the C-terminal domains between maspin and PAI-1 (plasminogen activator inhibitor type 1). The resulting stable transfectant clones expressing maspin/PAI-1 and PAI-1/maspin, respectively, did not undergo spontaneous apoptosis, and were similarly inhibited as maspin transfectant cells in motility assay. Interestingly, however, expression of both maspin/PAI-1 and PAI-1/maspin in MDA-MB-435 cells failed to sensitize these cells to STS-induced apoptosis. Taken together, our evidence provides new insights into the complex molecular mechanisms of maspin that may suppress breast tumor progression not only at the step of invasion and motility, but also by regulating tumor cell apoptosis. The sensitizing effect of maspin on apoptosis is to be contrasted by the pro-survival effect of several other serpins.

Evidence for a direct interaction between the tumor suppressor serpin, maspin, and types I and III collagen

Maspin (mammary serine protease inhibitor) was originally identified as a tumor suppressor protein in human breast epithelial cells and is a member of the serine proteases inhibitor (serpin) superfamily. It inhibits tumor cell motility and angiogenesis, and although predominantly cytoplasmic, it is also localized to the cell surface. In this study we have investigated the use of the yeast two-hybrid interaction trap to identify novel maspin targets. A target human fibroblast cDNA library was screened, and the alpha-2 chain of type I collagen was identified as a potential interactant. Binding studies with isolated proteins showed interaction between recombinant maspin and types I and III collagen but not other collagen subtypes, a profile strikingly similar to mouse pigment epithelium-derived factor (caspin), which is similarly down-regulated in murine adenocarcinoma tumors and is a potent inhibitor of angiogenesis. Kinetic analysis using an IAsys resonant mirror biosensor determined the dissociation constant of maspin for collagen type I to be 0.63 microm. Further two-hybrid interactions with maspin truncation constructs suggest that collagen binding is localized to amino acids 84-112 of maspin, which aligns with the collagen-binding region of colligin. A direct interaction between exogenous or cell surface maspin and extracellular matrix collagen may contribute to a cell adhesion role in the prevention of tumor cell migration and angiogenesis.

Tissue plasminogen activator is required for the growth, invasion, and angiogenesis of pancreatic tumor cells

BACKGROUND & AIMS

Overexpression of tissue-type plasminogen activator (t-PA) in exocrine pancreatic tumors might be a determinant of the aggressive biological behavior of these tumors.

METHODS

Endogenous t-PA production was suppressed by antisense oligonucleotides or transcripts in CAPAN-1 and RWP-1 cell lines. Reciprocally, the t-PA non-expressing BxPC-3 and PANC-1 cells were stably transfected to overexpress t-PA. Recombinant t-PA and chemical inhibitors were also used on these cells. Clones were assayed for invasion and growth in vitro and in vivo.

RESULTS

In vitro, specific inhibition of t-PA expression or activity significantly inhibited the proliferation of t-PA-producing RWP-1, CAPAN-1, and SK-PC-1 cells. Antisense constructs were used to generate RWP-1 clones stably suppressed for t-PA expression (AS clones). These clones had a significantly reduced invasion and proliferation on plastic and in soft agar. The addition of recombinant t-PA rescued the growth of the AS clones to parental levels and was mitogenic for other independent pancreas cell lines. This effect did not require plasmin activity. In athymic mice, RWP-1 AS clones produced tumors fivefold smaller than control clones. AS tumors contained a significantly reduced number of Ki67-positive nuclei, fewer mitotic cells, and a remarkably reduced angiogenic network. Finally, the generation of tetracycline-repressed t-PA transfectants in PANC-1 cells confirmed the activity of t-PA in invasion and proliferation in vitro and in vivo.

CONCLUSIONS

t-PA, in addition to its known role in invasion, plays other critical roles in pancreas tumor progression, stimulating cancer cell proliferation and tumor-associated angiogenesis.

Maspin expression in stage I and II oral tongue squamous cell carcinoma

BACKGROUND

A relatively high failure rate in the therapy of patients with early oral tongue squamous cell carcinomas (SCCs) is evidenced by untreated clinically negative neck lymph node metastasis. It is important to predict the malignant potential of oral tongue SCC in stage I and II patients, because the development of lymph node metastasis directly affects the prognosis of the patients.

METHODS

We evaluated maspin expression immunohistochemically in patients with stage I and II oral tongue SCCs and determined whether the expression level may be a useful factor in predicting metastatic potential and prognosis of these SCCs.

RESULTS

Clinical follow-up data showed a longer disease-free interval and overall survival periods for tumors immunohistochemically positive for maspin than for tumors negative for maspin, with the difference in disease-free interval being statistically significant (p =.01). The absence of maspin expression was found more frequently in cases of subsequent cervical lymph node metastasis than in cases without metastasis (p =.03).

CONCLUSIONS

Decreased maspin expression may be a significant factor associated with the metastatic potential of stage I and II oral tongue SCCs.

A novel function of tissue factor pathway inhibitor-2 (TFPI-2) in human glioma invasion

Human tissue factor pathway inhibitor-2 (TFPI-2) is a Kunitz-type serine protease inhibitor that inhibits plasmin, trypsin, chymotrypsin, cathepsin G, and plasma kallikrein but not urokinase-type plasminogen activator, tissue plasminogen activator, or thrombin. Preliminary findings in our laboratory suggested that the expression of TFPI-2 is downregulated or lost during tumor progression in human gliomas. To investigate the role of TFPI-2 in the invasiveness of brain tumors, we stably transfected the human high-grade glioma cell line SNB19 and the human low-grade glioma cell line Hs683 with a vector capable of expressing a transcript complementary to the full-length TFPI-2 mRNA in either sense (0.7 kb) or antisense (1 kb) orientations. Parental cells and stably transfected cell lines were analysed for TFPI-2 protein by Western blotting and for TFPI-2 mRNA by Northern blotting. The levels of TFPI-2 protein and mRNA were higher in the sense clones (SNB19) and decreased in the antisense (Hs683) clones than in the corresponding parental and vector controls. In spheroid and matrigel invasion assays, the SNB19 parental cells were highly invasive, but the sense-transfected SNB-19 clones were much less invasive; the antisense-transfected Hs683 clones were more invasive than their parental and vector controls. After intracerebral injection in mice, the sense-transfected SNB19 clones were less able to form tumors than were their parental and vector controls, and the antisense-Hs683 clones but not the parental or vector controls formed small tumors. This is the first study to demonstrate that down- or upregulation of TFPI-2 plays a significant role in the invasive behavior of human gliomas.

Maspin expression inversely correlates with breast tumor progression in MMTV/TGF-alpha transgenic mouse model

Maspin is a novel serine protease inhibitor (serpin) with tumor suppressive activity. To date, despite the mounting evidence implicating the potential diagnostic/prognostic and therapeutic value of maspin in breast and prostate carcinoma, the lack of a suitable animal model hampers the in vivo investigation on the role of maspin at different stages of tumor progression. In this study, we used MMTV/TGF-alpha transgenic mouse model to study the expression profile of maspin in mammary tumor progression. Histopathological examinations of MMTV/TGF-alpha transgenic mice revealed TGF-alpha expression leading to hyperproliferation, hyperplasia, and occasional carcinoma in mammary gland. Interestingly, when MMTV/TGF-alpha transgenic mice were breed to homozygocity, they also developed characteristic skin papillomas. Immunohistochemistry analysis of maspin expression in the breast tissues of TGF-alpha transgenic mice showed a direct correlation between down-regulation of maspin expression and tumor progression. The loss of maspin expression was concomitant with the critical transition from carcinoma in situ to invasive carcinoma. Subsequent in-situ hybridization analyses suggest that the down-regulation of maspin expression is primarily a transcriptional event. This data is consistent with the tumor suppressive role of maspin. Furthermore, our data suggests that MMTV/TGF-alpha transgenic mouse model is advantageous for in vivo evaluation of both the expression and the biological function of maspin during the slow multi-stage carcinogenesis of mammary gland.

Decline in the expression of the serine proteinase inhibitor maspin is associated with tumour progression in ductal carcinomas of the breast

Maspin is an inhibitor of serine proteinases with tumour suppressor activity. Its expression appears to be reduced in advanced stages of breast cancer. A large series of archival breast tissue specimens has been examined, including normal glands (n=7), fibrocystic change (n=22), ductal carcinoma in situ (DCIS, n=12), infiltrating carcinomas (n=128) and their lymph node metastases (n=65), using a specific monoclonal antibody. Myoepithelium invariably showed strong maspin expression. In epithelial cells, the strongest expression was found in normal breast and fibrocystic change. A significant stepwise decrease in maspin expression (p<0.0001) occurred in the sequence DCIS - invasive cancer - lymph node metastasis. However, a subset of infiltrating carcinomas showed strong maspin expression, significantly associated with a lower rate of lymph node metastasis at the time of diagnosis (p<0.01). This was independent of tumour size and grade. The in vivo observations presented here are in keeping with data obtained in prior in vitro experiments. Maspin emerges as an indicator of tumour progression and metastatic potential, and might be exploited to predict breast cancer prognosis. According to in vitro data, its tumour suppressor activity is likely to involve both the modulation of cell motility/invasiveness and the inhibition of angiogenesis.

Maspin--a novel protease inhibitor with tumor-suppressing activity in breast cancer

Maspin (mammary serpin) is a novel serine protease inhibitor related to the serpin family with a tumor-suppressing function in breast cancer. Maspin was originally identified from normal mammary epithelium by subtractive hybridization and might function as a class II tumor-suppressor gene. Maspin's decreased expression with increased level of malignancy and its loss in metastatic cells is regulated at the transcriptional level. Cytosin methylation and heterochromatinization in the promoter region might account for this down-regulation of maspin. Transfection of tumor cells with maspin cDNA inhibits invasion and motility and decreases tumor growth and metastatic ability in nude mice. Maspin interacts with the p53 tumor-suppressor pathway and function as an inhibitor of angiogenesis in vitro and in vivo. The progressive loss of expression of maspin during tumor progression makes this new protein an interesting diagnostic and prognostic marker. The re-expression of maspin by pharmacological intervention potentially offers a promising approach as a therapeutic option in breast cancer therapy.

Phylogeny of the Serpin Superfamily: Implications of Patterns of Amino Acid Conservation for Structure and Function

We present a comprehensive alignment and phylogenetic analysis of the serpins, a superfamily of proteins with known members in higher animals, nematodes, insects, plants, and viruses. We analyze, compare, and classify 219 proteins representative of eight major and eight minor subfamilies, using a novel technique of consensus analysis. Patterns of sequence conservation characterize the family as a whole, with a clear relationship to the mechanism of function. Variations of these patterns within phylogenetically distinct groups can be correlated with the divergence of structure and function. The goals of this work are to provide a carefully curated alignment of serpin sequences, to describe patterns of conservation and divergence, and to derive a phylogenetic tree expressing the relationships among the members of this family. We extend earlier studies by Huber and Carrell as well as by Marshall, after whose publication the serpin family has grown functionally, taxonomically, and structurally. We used gene and protein sequence data, crystal structures, and chromosomal location where available. The results illuminate structure–function relationships in serpins, suggesting roles for conserved residues in the mechanism of conformational change. The phylogeny provides a rational evolutionary framework to classify serpins and enables identification of conserved amino acids. Patterns of conservation also provide an initial point of comparison for genes identified by the various genome projects. New homologs emerging from sequencing projects can either take their place within the current classification or, if necessary, extend it.

Tamoxifen enhances myoepithelial cell suppression of human breast carcinoma progression in vitro by two different effector mechanisms

Our previous studies have indicated that myoepithelial cells surrounding ductal and acinar epithelium of glandular organs, such as the breast, exert multiple paracrine suppressive effects on incipient and developing cancers that arise from this epithelium. Myoepithelial cells and derived cell lines (HMS 1-6) exert these effects through the secretion of a number of different effector molecules that exert anti-invasive, anti-proliferative, and anti-angiogenic activities. Since previous basic and clinical studies have examined the role of estrogen agonists and antagonists on human breast cancer cells and because issues of hormone replacement therapy (HRT) and tamoxifen chemoprevention are such timely issues in breast cancer, we wondered whether or not hormonal manipulations might affect myoepithelial cells in vitro as far as their paracrine suppressive activities on breast cancer were concerned. The present in vitro study demonstrates that treatment of myoepithelial cells with tamoxifen but not 17beta-estradiol increases both maspin secretion and invasion-blocking ability. Furthermore tamoxifen but not 17beta-estradiol increases inducible nitric oxide synthase (iNOS) expression and nitric oxide (NO) production by myoepithelial cells when they are co-cultured with conditioned media from or breast carcinoma cells directly. This increased myoepithelial NO exerts both autocrine and paracrine antiproliferative effects which can be blocked by inhibition of iNOS. 17beta-Estradiol, however, competes with all of these suppressive effects of tamoxifen suggesting that the mechanism of tamoxifen action is estrogen receptor mediated. Myoepithelial cells lack ER-alpha but express ER-beta. Tamoxifen, but not 17beta-estradiol, increases AP-1 CAT but not ERE-CAT activity. Again, 17beta-estradiol competes with the transcription-activating effects of tamoxifen. These experiments collectively suggest that the actions of tamoxifen on the increased secretion of maspin and increased production of NO by myoepithelial cells are mediated through ER-beta and the transcription-activation of an ER-dependent AP-1 response element.

No grip, no growth: the conceptual basis of excessive proteolysis in the treatment of cancer

The formation of new bloodvessels, called angiogenesis, is critical for a tumour to grow beyond a few mm(3) in size. A provisional matrix promotes endothelial cell adhesion, migration, proliferation and survival. Synthesis and degradation of this matrix closely resemble processes that occur during coagulation and fibrinolysis. Degradation of the matrix and fibrinolysis are tightly controlled and balanced by stimulators and inhibitors of the plasminogen activation system. Here we give an overview of these processes during tumour progression. We postulate a novel way to inhibit angiogenesis by removal of the matrix through specific and localised overstimulation of the plasminogen activation system.

Identification of differentially expressed proteins between human hepatoma and normal liver cell lines by two-dimensional electrophoresis and liquid chromatography-ion trap mass spectrometry

In the previous study, the proteomes of the human hepatoma cell line BEL-7404 and the normal human liver cell line L-02 were separated by high resolution two-dimensional electrophoresis (2-DE). Image analysis revealed that 99 protein spots showed quantitative and qualitative variations that were significant (P < 0.01) and reproducible. Here we report the identification results of some of these protein spots. Protein spots excised from 2-D gels were subjected to in-gel digestion with trypsin, and the resulting peptides were measured by microbore high performance liquid chromatography - ion trap - mass spectrometry (LC-IT-MS) to obtain the tandem mass (MS/MS) spectra. Twelve protein spots were identified with high confidence using SEQUEST with uninterpreted MS/MS raw data. Besides inosine-5'-monophosphate dehydrogenase 2, heat shock 27 kDa protein, calreticulin and calmodulin, whose expression was elevated in hepatoma cells, glutathione-S-transferase P was identified from hepatoma cells in which its level was 18-fold higher compared to human liver cells. Two spots were identified as the homologs of reticulocalbin for the first time in hepatoma cells and their expression increased compared to liver cells. However, tubulin beta-1 chain and natural killer cell enhancing factor B were downregulated in hepatoma cells. A tumor suppressing serpin, maspin precursor, was identified from one spot whose quantity was much higher in the normal liver cell line. More interestingly, epidermal fatty acid-binding protein (E-FABP) and fatty acid-binding protein, adipocyte-type (A-FABP), were detected in liver cells but not in hepatoma cells. The functional implication of the identified proteins was discussed.

High tumoral maspin expression is associated with improved survival of patients with oral squamous cell carcinoma

Maspin, a member of the serpin family of protease inhibitors, is known to have tumor-suppressor functions. However, the association between its expression level and survival has not been demonstrated in human cancer. Using the immunohistochemical technique to examine the expression levels of maspin in 44 cases of oral squamous cell carcinoma (SCC), we found that 66% of the cases expressed low to intermediate levels of maspin and 34% of the cases expressed high levels of maspin. We further examined maspin protein expression in a series of six SCC cell lines from the head and neck, and found that all but one expressed low or no maspin protein. We also compared the clinicopathological features of the oral SCC cases with the maspin expression level, and found that high maspin expression was associated with the absence of lymph node metastasis. More importantly, we showed that higher maspin expression was significantly associated with better rates of overall survival, suggesting that high maspin expression may be a favorable prognostic marker for oral SCC.

Epigenetic silencing of maspin gene expression in human breast cancers

Maspin is a tumor suppressor whose expression is lost in many advanced breast cancers. Maspin has been shown to inhibit cell motility, invasion and metastasis; however, its precise role in normal mammary epithelium remains to be elucidated. Although expression of maspin mRNA is low or absent in most human breast cancer cells, the maspin gene is rarely re-arranged or deleted. We hypothesized that aberrant cytosine methylation and chromatin condensation of the maspin promoter participates in the silencing of maspin expression during neoplastic progression. To test this hypothesis, we compared cultured normal human mammary epithelial cells (HMECs) to 9 cultured human breast cancer cell lines. HMECs expressed maspin mRNA and displayed a completely non-methylated maspin gene promoter with an open chromatin structure. In contrast, 7 of 9 breast cancer cell lines had no detectable maspin expression and 6 of these 7 maspin-negative breast cancer cell lines also displayed an aberrant pattern of cytosine methylation of the maspin promoter. Interestingly, the maspin promoter was completely methylated in maspin-negative normal peripheral blood lymphocytes. This indicates that the maspin promoter is not a functional CpG island and that cytosine methylation of this region may contribute to normal tissue-restricted gene expression. Chromatin accessibility studies with MCF-7 cells, which lack maspin expression and have a methylated maspin promoter, showed a closed chromatin structure compared with HMECs. Moreover, maspin gene expression could be re-activated in MCF-7 cells by treatment with 5-aza-2;-deoxycytidine, a DNA demethylating agent. Thus, aberrant cytosine methylation and heterochromatinization of the maspin promoter may silence maspin gene expression, thereby contributing to the progression of human mammary cancer.

p53 regulates the expression of the tumor suppressor gene maspin

Maspin has been shown to inhibit tumor cell invasion and metastasis in breast tumor cells. Maspin expression was detected in normal breast and prostate epithelial cells, whereas tumor cells exhibited reduced or no expression. However, the regulatory mechanism of maspin expression remains unknown. We report here a rapid and robust induction of maspin expression in prostate cancer cells (LNCaP, DU145, and PC3) and breast tumor cells (MCF7) following wild type p53 expression from an adenovirus p53 expression vector (AdWTp53). p53 activates the maspin promoter by binding directly to the p53 consensus-binding site present in the maspin promoter. DNA-damaging agents and cytotoxic drugs induced endogenous maspin expression in cells containing the wild type p53. Maspin expression was refractory to the DNA-damaging agents in cells containing mutant p53. These results, combined with recent studies of the tumor metastasis suppressor gene KAI1 and plasminogen activator inhibitor 1 (PAI1), define a new category of molecular targets of p53 that have the potential to negatively regulate tumor invasion and/or metastasis.

Adenovirus endopeptidase hydrolyses human squamous cell carcinoma antigens in vitro but not ex vivo

The serpins SCCA1 and SCCA2 are highly expressed in the epithelium of the conducting airways, a common site of infection by group C adenoviruses, such as human adenovirus type 2 (Ad2). Based on the common location we examined a possible interaction between them. In vitro experiments with recombinant proteins showed that SCCA1 inhibited the viral protease in a dose-dependent manner. Both serpins were cleaved in a manner consistent with hydrolysis within their reactive site loop, without the formation of an SDS-resistant complex, as in the case of papain. Infection of SCCA1-expressing cells did not result in the cleavage of SCCA1, nor was the yield of infectious virus affected as compared to SCCA1-negative parental cells. This may be due to differential localization, the serpin being cytoplasmic and viral protease being nuclear. Surprisingly, however, virus infection, which tends to inhibit host protein synthesis, caused a significant increase in SCCA1 expression well into the late phase of infection.

Maspin is an angiogenesis inhibitor

Maspin, a unique member of the serpin family, is a secreted protein encoded by a class II tumor suppressor gene whose downregulation is associated with the development of breast and prostate cancers. Overexpression of maspin in breast tumor cells limits their growth and metastases in vivo. In this report we demonstrate that maspin is an effective inhibitor of angiogenesis. In vitro, it acted directly on cultured endothelial cells to stop their migration towards basic fibroblast growth factor and vascular endothelial growth factor and to limit mitogenesis and tube formation. In vivo, it blocked neovascularization in the rat cornea pocket model. Maspin derivatives mutated in the serpin reactive site lost their ability to inhibit the migration of fibroblasts, keratinocytes, and breast cancer cells but were still able to block angiogenesis in vitro and in vivo. When maspin was delivered locally to human prostate tumor cells in a xenograft mouse model, it blocked tumor growth and dramatically reduced the density of tumor-associated microvessels. These data suggest that the tumor suppressor activity of maspin may depend in large part on its ability to inhibit angiogenesis and raise the possibility that maspin and similar serpins may be excellent leads for the development of drugs that modulate angiogenesis.

Maspin plays an important role in mammary gland development

Maspin is a unique member of the serpin family, which functions as a class II tumor suppressor gene. Despite its known activity against tumor invasion and motility, little is known about maspin's functions in normal mammary gland development. In this paper, we show that maspin does not act as a tPA inhibitor in the mammary gland. However, targeted expression of maspin by the whey acidic protein gene promoter inhibits the development of lobular-alveolar structures during pregnancy and disrupts mammary gland differentiation. Apoptosis was increased in alveolar cells from transgenic mammary glands at midpregnancy. However, the rate of proliferation was increased in early lactating glands to compensate for the retarded development during pregnancy. These findings demonstrate that maspin plays an important role in mammary development and that its effect is stage dependent.

Three-state unfolding and self-association of maspin, a tumor-suppressing serpin

Maspin is a tumor suppressor protein expressed by normal human mammary epithelium but not by many breast tumor cell lines. Recombinant human maspin (rMaspin) inhibits tumor cell motility, invasion, and metastasis and thus has potential value as an anti-cancer therapeutic. Maspin is a member of the serpin family and, although the molecular mechanism by which maspin acts is unknown, recent work suggests that tissue plasminogen activator is a potential target. A puzzling observation in previous cell culture studies was loss of rMaspin activity at higher protein concentrations. One hypothesis to explain these results is self-association of rMaspin at the higher concentrations, which would be consistent with the tendency of serpins to form noncovalent polymers. This hypothesis is addressed by examining the relationship between rMaspin stability and self-association. Urea denaturation of rMaspin at pH 7 and 25 degrees C and at protein concentrations ranging from 0.01 to 0.2 mg/ml has been monitored by circular dichroism and intrinsic tryptophan fluorescence. Denaturation profiles show a protein concentration dependence and indicate the presence of at least one unfolding intermediate. The results suggest that destabilization of native monomeric rMaspin leads to partial unfolding and formation of an intermediate which can self-associate.

New, sensitive fluorogenic substrates for human cathepsin G based on the sequence of serpin-reactive site loops

Cathepsin G has both trypsin- and chymotrypsin-like activity, but studies on its enzymatic properties have been limited by a lack of sensitive synthetic substrates. Cathepsin G activity is physiologically controlled by the fast acting serpin inhibitors alpha1-antichymotrypsin and alpha1-proteinase inhibitor, in which the reactive site loops are cleaved during interaction with their target enzymes. We therefore synthesized a series of intramolecularly quenched fluorogenic peptides based on the sequence of various serpin loops. Those peptides were assayed as substrates for cathepsin G and other chymotrypsin-like enzymes including chymotrypsin and chymase. Peptide substrates derived from the alpha1-antichymotrypsin loop were the most sensitive for cathepsin G with kcat/Km values of 5-20 mM-1 s-1. Substitutions were introduced at positions P1 and P2 in alpha1-antichymotrypsin-derived substrates to tentatively improve their sensitivity. Replacement of Leu-Leu in ortho-aminobenzoyl (Abz)-Thr-Leu-Leu-Ser-Ala-Leu-Gln-N-(2, 4-dinitrophenyl)ethylenediamine (EDDnp) by Pro-Phe in Abz-Thr-Pro-Phe-Ser-Ala-Leu-Gln-EDDnp produced the most sensitive substrate of cathepsin G ever reported. It was cleaved with a specificity constant kcat/Km of 150 mM-1 s-1. Analysis by molecular modeling of a peptide substrate bound into the cathepsin G active site revealed that, in addition to the protease S1 subsite, subsites S1' and S2' significantly contribute to the definition of the substrate specificity of cathepsin G.